The function takes a string input and shifts each alphabetical character in the string by 7 positions along the alphabet, wrapping around when necessary. The function doesn't modify non-alphabetical characters.

[CODE]:
```python
def shift_by_7(input_str):
    output_str = []
    for char in input_str:
        if 'A' <= char <= 'Z':
            output_str.append(chr(((ord(char) - 65 + 7) % 26) + 65))
        elif 'a' <= char <= 'z':
            output_str.append(chr(((ord(char) - 97 + 7) % 26) + 97))
        else:
            output_str.append(char)
    return ''.join(output_str)
```

Let me know if you need any more information or help.